Man, how lame. Safire this week just quotes letters speculating on the history of an idiom or two. Don't even bother if the print issue is sitting in front of you. (He does cite the Historical Dictionary of American Slang, so our Alert Reader — who's earned caps by now — wins.)
Much more worth your time is Jan Freeman's most recent blog post, here, playing with Gender Genie. I too wonder what samples they drew on. The most recent post on this blog (by our contributor Joe) comes out clearly masculine, but my own posts are mixed. Some stuff that probably reads like male prose to a human (like some earlier Safire Watch posts that I thought had an edge to them) get rated as feminine, to my surprise. The last post on Everett counts as the most masculine of the ones I checked.
You have to figure this is going to be very rough and marginally accurate. And looking at how words/forms like are, she, a, the are flagged (run a text through and you'll see), you end up figuring, yup, this is a messy process. It's worth keeping an eye on, though, as they sharpen this tool.